Apparatus and method for determining position of drilling tool during drilling

ABSTRACT

An apparatus and method of determining the position of a drilling tool during drilling is provided. The apparatus includes a magnetic source mounted to a rotating drilling tool and at least two magnetometers, which are located outside a drilled hole. Sensing data of a rotating magnetic field is transmitted from the magnetometers to a control unit provided with a position calculation algorithm. The control unit is also provided with position data of the magnetometers and a reference position of the drilling tool. The control unit compares the received sensing data when the drilling tool is in the reference position and when being moved to a new position. Phase angles are then detected from the sensing data. The algorithm utilizes the phase angles and the known positions of the magnetometers and the reference point when calculating the changed position.

RELATED APPLICATION DATA

This application claims priority under 35 U.S.C. § 119 to EP Patent Application No. 19170203.4, filed on Apr. 18, 2019, which the entirety thereof is incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to an apparatus configured to determine location of a drilling tool during rock drilling, wherein the apparatus utilizes magnetic field measurements. The disclosure further relates to a rock drilling rig provided with the disclosed apparatus and to a method and computer program product for determining location of a drilling tool during rock drilling.

BACKGROUND

In mines and at other work sites different type of rock drilling rigs are used for drilling drill holes to rock material. The drilling rig includes a drilling unit provided with a drilling machine and a drilling tool is connected thereto. During the drilling, the drilling tool is subjected to different forces whereby the drilling tool may move side wards and away from the planned drilling line. This causes the finished drill hole to deviate from the designed drill hole and may cause problems to procedures following the drilling. Therefore, different devices and methods are disclosed for examining properties of the drilled holes.

However, sensing properties of the drill hole during the drilling is problematic. Conditions inside the drill hole during the drilling are extremely harsh. Thereby no satisfying solution for tracking position of the drilling tool during the drilling is presently known.

SUMMARY

An object of the present disclosure is to provide a novel and improved apparatus and method for tracking the drilling tool during the drilling. A further object is to provide a rock drilling rig equipped with such apparatus and a computer program for implementing the disclosed solution.

An idea of the disclosed solution is that position of a drilling tool is monitored during the drilling process.

The solution discloses a magnetic tracking system for sensing sideward or lateral position movements of the drilling tool. In the disclosed solution, position sensing of the drilling tool is based on magnetism.

The apparatus includes at least one magnetic source mounted to a rotating drilling tool. Further, the apparatus has at a minimum only two magnetometers and the magnetometers are located outside the drill hole.

Sensing data of rotating magnetic field is transmitted from the magnetometers to a control unit provided with a position calculation algorithm. The control unit is also provided with basic data for the calculation, wherein the basic data includes pose of the magnetometers and the position of a reference position of the drilling tool. The control unit compares the received sensing data when the drilling tool is in the reference position and when being moved to a new position. Phase angles are then detected from the sensing data. If no phase angles occur between the reference data and the sensing data, then the drilling tool has not changed its position. Typically, some position change occurs, and the algorithm may utilize the detected phase angles, the known poses of the magnetometers and the known position of the reference point when calculating the changed position.

An advantage of the disclosed solution is that there is no need to use downhole instruments to determine the heading of a borehole. A further advantage is that the disclosed solution provides a measurement-while-drilling (MWD) solution i.e. the measurements are done during the drilling of the drill holes.

The disclosed system based on magnetism is suitable for all kind of drilling circumstances, except situations where magnetic material or iron ore disturbs the sensing of the rotating magnetic field of the drilling tool.

A further advantage is that the magnetic field can be sensed from a very long distance. The rock material being drilled may be nonhomogeneous and may have different kinds of rock material and different rock qualities, and still the sensing is not hampered when the disclosed solution is used.

Since the magnetometers are located outside the drill hole being examined, positioning of the magnetometers is easy and quick to make, and further, there are plenty of optional locations to be selected for the positions of the magnetometers.

The solution is also inexpensive, since no extensive re-design needs to be done for the drilling equipment. Providing the drilling tool with one or more magnetic sources is enough and requires only minor modifications or extras to the existing drilling tools. It may even be possible to retrofit the magnets to the existing drilling components.

Further, the disclosed solution requires only two magnetometers at a minimum, whereby the number of the relatively expensive magnetometers is limited and the apparatus may be inexpensive.

According to an embodiment, the reference data is produced prior to initiating the actual drilling. The drilling tool with the magnetic source is then positioned at a desired drill hole position and is aligned according to the desired drill hole direction. The drill hole position and direction may be pre-determined in a drilling pattern or excavation plan. The position of the drilling tool may be used as the mentioned reference point, since its position is accurately known by the rock drilling rig. A drilling unit may be supported against a rock surface and the drilling tool is rotated around its drilling axis. Rotating speed may be the same used in the actual drilling. The rotating speed is sensed by sensors of the rock drilling rig.

According to an embodiment, the reference data may be produced at any time instance, even after the actual drilling has already been initiated. However, also in this case, the position of the drilling tool and the magnetic source needs to be detectable in order to be used as the reference point.

According to an embodiment, the rotation rate of the drilling tool is the same in the initial reference measurement and in the actual measurement, or alternatively, the changed rotation speed is taken into consideration in the determination of the phase angles. In other words, the rotation speed is kept constant, or the control unit compensates for the possible changed rotation speed so that a comparison of the reference sensing data and the actual sensing data is possible.

According to an embodiment, the magnetic flux sensed by the magnetometers is examined in function to the rotation angle of the drilling tool. Thus, the examination is not executed in function to time.

According to an embodiment, the control unit is configured to calculate two-dimensional (2D) data on the position of the drilling tool on the basis of the detected phase angles and the input positions of the magnetometers and the reference position of the magnetic source. In other words, the control unit calculates position changes in transverse directions relative to the drilling axis. The control unit may examine the situation in a two-dimensional plane.

According to an embodiment, the apparatus is without any electrical sensing devices mounted to the drilling tool. Thereby, no electrical sensing devices are inserted together with the drilling tool inside the drill hole during the drilling.

According to an embodiment, the apparatus may be implemented in rotary drilling, as well as, in percussion drilling. Further, the apparatus is suitable to be used in connection with top hammer and down-the-hole drilling solutions. The disclosed solution may also be implemented in surface and underground drilling.

According to an embodiment, the measurements and the calculation of the position data are executed in real-time during the drilling.

According to an embodiment, the control unit is configured to take into consideration only rotating magnetic fields, the rotating speed of which corresponds to the rotational speed of the drilling tool. Thereby, possible other magnetic fields may be filtered, separated and possibly ignored when seeking the rotating magnetic field of the drilling tool.

According to an embodiment, the frequency of the detected alternating magnetic field is equal to the rotation speed of the drilling tool.

According to an embodiment, the disclosed solution may be implemented regardless of direction and purpose of the drill hole. The disclosed measurement may then be executed for vertical drilling when downward or upward directed drill holes are drilled. Further, the measurement is also suitable for substantially horizontal drilling, such as to face drilling in tunneling.

According to an embodiment, positions of the magnetometers may be freely selected as long as their position and orientation is determined and input to the control system before initiating the measurements.

According to an embodiment, the apparatus may have three, four or even more magnetometers, whereby two is the minimum number of the magnetometers. When implementing greater number of magnetometers, the accuracy of the measurements may be verified by comparing several sensing results. This embodiment may also be useful when operating at work sites where issues causing disturbances to the magnetic fields occurs.

According to an embodiment, the control unit is provided with a computer program product or algorithm for executing the needed calculations. The calculation program or software implements triangulation and trigonometry in the calculation.

According to an embodiment, the received sensing data is examined by determining maximum strength values of the received magnetic field data and corresponding rotation angle of the magnetic source relative to the examined magnetometer at that peak value is detected. Further, the phase angle between the reference sensing data and any new sensing data is determined by comparing the rotation angles of the detected maximum strength values. In other words, this embodiment utilizes sensed peak values.

According to an embodiment, the control unit is configured to detect phase difference between the reference sensing data and an actual sensing data. Magnitude of the phase difference indicates magnitude of change of position of the magnetic source from the known reference position. In other words, magnitude of the detected phase difference indicates magnitude of the phase angle. The phase difference may be detected by examining the peak values, for example.

According to an embodiment, the control unit may or may not detect the above mentioned phase angle and phase difference by examining the peak values of the sensed magnetic field. Alternatively, minimum strength values may be used for the detection.

According to an embodiment, a further alternative for determining the phase angles and phase differences is to analyze a wider sample of the sensing data or to continuously monitor the sensing data for detecting the phase difference and phase angle. Then, not only peak or other single values are examined, but instead the analysis includes longer periods of time. Alternatively, more than one wave lengths may be examined

The analysis takes into account one or more wave lengths sensed before momentum of the calculation. The calculation of the phase angles may be based on signal processing methods. Alternatively, or in addition to, mathematical analysis, such as vector algebra and Fourier transformation, may be implemented for determining the phase differences and phase angles. In summary, there are alternative ways for analyzing the sensing data of the magnetometers.

According to an embodiment, the magnetometers are located on a rock surface surrounding the drill hole being drilled. Then mounting of the magnetometers on the surface is easy and quick.

According to an embodiment, the magnetometers are located on the surface level. Thus, data transfer between the magnetometers and the control unit is easy to arrange. Further, when the magnetometers are surface mounted, they are not subjected to harsh underground circumstances. Thereby, it is possible to use standard commercially available magnetometers for the measuring.

According to an embodiment, the magnetometers are located on a horizontal or substantially horizontal plane.

According to an embodiment, the known positions of magnetometers and the reference position of the magnetic source define a two-dimensional plane where the position change of the magnetic source is examined The positions may be defined in X-Y coordinates.

According to an embodiment, transverse distances of the magnetometers from the drill hole are selected in relation to the designed depth of the finished drill hole. The distances are usually several meters, and may be up to 10-20 meters, for example.

According to an embodiment, transverse distances of one or more magnetometers from the drill hole may, in special cases, be relatively small. Then one or more magnetometers may be located nearby the drill hole, but in anyway, outside the drill hole.

According to an embodiment, the magnetometers are mounted to the rock drilling rig. Then the magnetometers may be mounted on a carrier, to a drilling boom or to a drilling unit, for example. Further, the magnetometers may be mounted to arms so that they may be located at greater lateral distance from the drilling tool. Due to the arms, the magnetometers may be positioned at desired locations around the drilling tool. The arms may be movable so that the position and distance relative to the drilling tool may be changed. The arms may also have a retracted transport or storage position and an extended sensing or operational position.

According to an embodiment, the disclosed solution utilizes three directional magnetometers capable of sensing magnetic flux in three components, x, y and z components. When position and orientation of the magnetometers is known by the measuring system, then selected sensed components may be examined when determining the phase angles.

According to an embodiment, in addition to the detected two-dimensional change of position of the magnetic source, a third dimension is also included. Thus, drilling depth is measured and is included in the examination. This way three-dimensional position data can be produced. The drilling depth may also be called as an advance distance.

According to an embodiment, the data on advanced distance is produced by means of a distance sensing device external to the apparatus. It should be appreciated that there are several alternative ways and principles for sensing the drilling depth.

According to an embodiment, the distance sensing device is mounted to a drilling unit of the rock drilling rig. The drilling unit manipulates the drilling components during the drilling and the distance sensing unit locating in the drilling unit may monitor feeding of the drilling components.

According to an embodiment, the distance sensing device is configured to determine distance between the drill bit and a drill hole opening or mouth.

According to an embodiment, the solution aims to detect bending of the drilling tool during the drilling and the caused deviations in straightness of the drilled hole. In order to detect the bending, several measurements at different drill hole depths needs to be executed. Then several measuring points locating at different advance distances of the magnetic source inside the drilled hole are used. The number and depth of the measuring points may be selected case-by-case. At each measuring point sensing data received from the magnetometers is analyzed and position data is calculated. The control unit compares the calculated position data and determines the bending on the basis of the detected differences in the calculated position data.

According to an embodiment, the determined data on bending is implemented in determining quality of the rock drilling and determining quality of the finished drill hole.

According to an embodiment, the determined data on bending is implemented during the drilling for initiating and controlling corrective measures. The corrective measures may include directional drilling, wherein the drilling is actively steered for compensating the detected bending of the drilling tool and the drilled hole. A still possible implementation is to steer the drilling tool purposely so that it becomes bent, and to thereby produce drill holes with desired non-linear advance profile or side profile.

According to an embodiment, the control unit is configured to produce coordinate data on the changed position of the magnetic source. Then the control unit is provided with data on coordinates of the magnetometers and the reference position in a work site coordinate system.

According to an embodiment, the above mentioned work site coordinate system may be a mine coordinate system or a project coordinate system.

According to an embodiment, the above mentioned position data with the coordinates may be linked via the work site coordinate system to a drilling plan, charging plan or reinforcing plan.

According to an embodiment, the control unit is configured to calculate position of a face surface of the drilling tool in response to the input position data of the magnetic source relative to the face surface, whereby the position of the drilling tool is examined as the position of the face surface.

According to an embodiment, the position of the above-mentioned face of the drilling tool equals the position of a bottom of the drill hole during the drilling phase. The position of the drill hole bottom is important especially when charging the drilled hole with explosives.

According to an embodiment, the control unit is provided with one or more processors configured to execute a position detection algorithm, the execution of which is configured to calculate the position of the magnetic source in response to the received sensing data of the magnetometers and the input reference and position data.

According to an embodiment, the position detection algorithm, computer program product or software is configured to implement triangulation and trigonometry in the calculation.

According to an embodiment, the control unit is configured to execute the position determination without comparing strength of the detected magnetic fields.

According to an embodiment, the strength of the detected magnetic field has no importance to the position detection since the detection is based on determining phase angles of the sensed magnetic fields when the magnetic source is at the reference point and at a changed new position. The rotating magnetic source generates the alternating magnetic field which is sensed by the magnetometers locating at different positions. The rotating magnetic field is aligned with the magnetometers at different phases. When at least two phase angles indicating the position change from the known reference point are detected, then the new location can be calculated.

According to an embodiment, the magnetometers may be located at different distances from the drill hole, and further, the rock material surrounding the drill hole may have different properties. Therefore, the strength of the magnetic field detected by the separate magnetometers is different. When the position detection is based on the phase angle, and not to strength of the magnetic field, then attenuation of the magnetic field in the rock material has no influence to the disclosed positioning sensing procedure.

According to an embodiment, the magnetic source is a permanent magnet. The permanent magnet is inexpensive and its mounting to the drilling tool is relatively simple.

According to an embodiment, the magnetic source is an electromagnet or a coil.

According to an embodiment, the magnetic source is mounted to a drill bit locating at a distal end of the drilling tool.

According to an embodiment, the magnetic source is mounted to a drill rod or tube.

According to an embodiment, the magnetic source is mounted to an adapter piece, which is located between the drill bit and the drill rod or tube. The adapter piece may be a component that is designed especially for receiving the one or more magnetic sources.

According to an embodiment, the magnetic source is covered or surrounded with non-ferromagnetic material. The material may be resilient material and may thereby serve as protective material layer. The surrounding material may dampen forces directed to the magnetic source during the operation and may thereby lengthen life time of the magnetic source. Especially in percussion drilling the dampening feature may be found useful as the magnetic field penetrates well through the non-ferromagnetic material.

According to an embodiment, when the drilling tool or its drilling component is made of ferromagnetic material, it may have a recess on its radial outer surface for receiving the magnetic source together with surrounding non-ferromagnetic filling material. When a special adapter element is applied between the drill bit and a drill rod or tube, then the adapter may be made of stainless steel, or another non-ferromagnetic steel material.

According to an embodiment, the disclosed apparatus and solution may be implemented for examining straightness of the already drilled drill holes. The drilling tool with the magnetic source is then positioned at first to a reference location, such as at a mouth opening of the drill hole, for producing the reference data. Thereafter, the drilling tool is moved longitudinally to desired one or more drill hole depths and a change of position of the drilling tool and the magnetic source is calculated as disclosed further herein.

According to an embodiment, the disclosed apparatus and solution may be implemented in detection of the drill hole straightness without calculating absolute positions of the magnetic source. Instead of the calculated position coordinates, the control unit may be provided with a limit value for the maximum deviation of the phase angle or phase difference between the sensing data of the actual drilling and the reference data. When the limit value is exceeded then the drilling may be terminated, a warning signal may be generated, or corrective measures may be initiated.

According to an embodiment, the disclosed measuring principle may be implemented in connection with a special measuring means. The magnetic source is then mounted to a measuring instrument, probe, component or element, which may be rotated around its longitudinal axis and may be moved in longitudinal direction inside a drill hole. In other words, this embodiment does not include any drilling tool. The disclosed embodiment may be a special measuring device intended for measuring straightness of the already drilled drill holes.

The foregoing summary, as well as the following detailed description of the embodiments, will be better understood when read in conjunction with the appended drawings. It should be understood that the embodiments depicted are not limited to the precise arrangements and instrumentalities shown. The above disclosed embodiments may be combined in order to form suitable solutions having those of the above features that are needed.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic side view of a rock drilling rig.

FIG. 2 is a schematic diagram presenting components of the disclosed apparatus.

FIG. 3 is a schematic side view of a drilling tool and its components provided with magnetic sources.

FIG. 4 is a schematic side view of a drilling tool at a bottom of a drill hole.

FIG. 5 is a schematic side view of a magnetic source surrounded by means of non-ferromagnetic protection material.

FIG. 6 is a schematic diagram showing a control unit intended for executing position detection.

FIG. 7 is a schematic top view of a measuring arrangement comprising two magnetometers and a magnetic source mounted to a rotating drilling tool.

FIG. 8 is a schematic graph of magnetic field measurements taken by a magnetometer at a reference position and at a changed position of the magnetic source.

FIG. 9 is a schematic side view of a measuring arrangement for detecting drill hole straightness.

FIG. 10 is a schematic side view showing an alternative mounting arrangement for magnetometers.

FIG. 11 is a schematic representative graph of magnetic field measurements and determination of a phase angle.

For the sake of clarity, the figures show some embodiments of the disclosed solution in a simplified manner. In the figures, like reference numerals identify like elements.

DETAILED DESCRIPTION

FIG. 1 shows a rock drilling rig 1 for drilling drill holes 2. The rock drilling rig 1 includes a movable carrier 3 and one or more drilling booms 4 connected to the carrier 3. The drilling boom 4 is provided with a drilling unit 5 having a feed beam 6 and a rock drilling machine 7 supported movably on it. A drilling tool 8 is connectable to the rock drilling machine 7 and may be rotated in a direction R around drilling axis 9 by means of a rotation device of the rock drilling machine 7.

At a distal end of the drilling tool 8 is a drill bit 10. The rock drilling machine 7 may have a percussion device for generating impact pulses to the drilling tool 8. The percussion device may be located either in connection with the drilling machine 7 or at a distal end portion of the drilling tool, whereby the percussive rock drilling may be top hammer drilling or down-the-hole drilling. A further alternative is that the drilling is rotary drilling without percussion. The rock drilling machine 7 is fed in the direction F during the drilling by means of a feed device, which is not shown in FIG. 1.

The rock drilling rig 1 of FIG. 1 is intended for vertical surface drilling and may be equipped with the apparatus as disclosed herein. However, the solution of FIG. 1 is only one drilling application. The disclosed solution may also be utilized in other drilling solutions, such as in long hole drilling, face drilling, bench drilling, etc.

FIG. 2 discloses an apparatus 11 for positioning sensing of a drilling tool. The apparatus 11 includes one or more control units CU for analysing sensing data received from two or more magnetometers 12. The apparatus 11 further includes one or more magnetic sources 13 mounted to a rotatable drilling tool. The apparatus 11 may also be provided with depth sensing means 14 for determining an advance distance of the magnetic source inside a drill hole.

FIG. 3 discloses a drilling tool 8, which may include several drilling components connected to each other. The drilling tool 8 may have one or more drilling rods 15 or tubes and a drill bit 10. Between the rod 15 and the drill bit 10 may be an adapter piece 16. At least one of the components 15, 16, 10 is provided with at least one magnetic source 13. The magnetic source 13 is mounted so that axis of magnetic field 17 is transverse to drilling axis 9 of the drilling tool 8. It is possible to use several magnetic sources 13 in one component or provide several components with them.

FIG. 4 discloses a distal end part of a drilling tool 8. Between drill bit 10 and drill rod 15 is an adapter piece 16 made of non-ferromagnetic material and having a permanent magnet 13. The magnet 13 is then close to a face of the drill bit and a bottom 18 of a drill hole 2. The distance between the magnet 13 and the bottom 18 is known and the position of the drill hole bottom 18 may thereby be sensed by the disclosed solution.

FIG. 5 discloses that around a magnetic source 13 may be a protective material 19, which may be of non-ferromagnetic material. The protective material 19 may dampen mechanical forces directed to magnetic source 13 and may also encapsulate it against harsh conditions occurring inside the drill hole. The protective material 19 may also participate in fastening of the magnetic source 13.

FIG. 6 discloses a control unit CU having a processor 20 for executing a position detection program 21 input to the control unit CU. The control unit CU further includes memory means 22 for storing programs and data, and data communication means 23 for communicating with servers and other control units, such as with a drilling control unit of a rock drilling rig or with a mine control system.

The control unit has input means 24 for receiving position and orientation data on magnetometers 25. Reference data 26 including data on the reference position 27 of the magnetic source and reference sensing data 28 of the magnetometers is also input to the control unit before executing actual position measures. When the position of the drilling tool is tracked sensing data produced by the magnetometers 29 is input to control unit CU. Also, data on the advance distance of the tracked magnetic source 30 may be input.

The control unit analyses the input data and outcomes of the analyses and calculations executed by the processor 20 are transmitted through output means 31 to desired systems, servers and control units. The control unit CU may produce position data on the drilling tool 32, data on drill hole straightness or bending of the drilling tool 33, control commands for steering and controlling the drilling process 34 and updates 35 to drilling patterns, excavation plans and charging plans, for example.

FIG. 6 further discloses that rotation data 41 of the drilling tool and the included magnetic source may be sensed and input to the control unit CU. The rotation data 41 may be determined by means of separate sensing devices, which are located in connection with the drilling unit. The rotation data 41 of the drilling is known by the system since rotation is one control parameter of the drilling process. However, the rotation data 41 may also be determined by analyzing sensing results received from the magnetometers.

FIG. 7 illustrates the disclosed measuring principle, wherein the drilling tool 8, provided with a magnetic source 13, is rotated and rotation angles A can be sensed by a first magnetometer 12 a and a second magnetometer 12 b. Reference data needed in the calculation can be produced by rotating the drilling tool 8 at a known reference position 27. Then the rotating magnetic field is sensed by the magnetometers 12 a and 12 b and first reference sensing data 28 a and second reference sensing data 28 b are generated. The reference data may be generated before the actual drilling is initiated.

During normal drilling actual sensing data 29 a, 29 b is produced by the magnetometers 12 a, 12 b. If the drilling tool 8 changes its position from the known reference point 27 in the examined plane and moves in direction T to a new position 36, then a first phase angle B exists between the first reference sensing data 28 a and the actual first sensing data 29 a, and correspondingly a second phase angle C exists between the second reference sensing data 28 b and the actual second sensing data 29 b. This is due to changed alignment between the first magnetometer 12 a and the magnetic source 13, and correspondingly between the second magnetometer 12 b and the magnetic source 13.

Further, positions 25 a, 25 b of the magnetometers 12 a, 12 b are known by the tracking system, whereby position data of the new position 36 can be calculated. The actual calculation is based on normal trigonometry, which is well known by one skilled in the art and is therefore not described in detailed herein.

In FIG. 7 lines 28 a-28 c and 29 a-29 b are used only to illustrate the sensing data. The actual sensing data comprises signals and has a typical sine wave form as it is disclosed in FIGS. 8 and 11. Thus, FIG. 7 is a simplified presentation for improving understanding the disclosed solution.

FIG. 8 discloses graphs of the first reference sensing data 28 a and the first actual sensing data 29 a. The magnitude or strength H of the sensed magnetic field in relation to the rotation angle A of the drilling tool is illustrated. As can be noted, the reference data 28 a and the sensing data 29 a can be illustrated as sine waves. When examining the sine waves, for example peak values 37 a and 37 b, it can be noted that there is a shift in the peak values 37 a, 37 b. In other words, the curves have a phase difference. The phase difference corresponds to the first phase angle B. The phase angle C can be illustrated and determined in a similar manner

FIG. 9 discloses a measuring principle for determining bending of a drill hole 2. The drilling tool 8 is positioned at a start point of a drill hole and this point can be used as a reference point. The positioning system of the rock drilling rig knows the accurate position of the drilling tool at the start point. Magnetometers 12 a and 12 b are mounted on a rock surface 38 and they may be located at different distances L1 and L2 from the drilling tool 8. Positions of the magnetometers 12 a, 12 b and the drilling tool 8 positioned at the reference point can be determined in a work site coordinate system 39, for example. When the drilling begins, the position of the drilling tool 8 is determined by examining rotating magnetic field generated by a magnetic source 13. Simultaneously, the advance distance of the drilling tool 8 is sensed by means of sensor 14. When the position measurements are executed at several measuring points Mp1-Mp3, positions at different advance distances Ad1-Ad3 are detected. On the basis of the obtained data, straightness of the drill hole 2 can be examined in a control unit CU.

FIG. 10 discloses a solution, wherein magnetometers 12 a, 12 b are connected to a drilling unit 5 by means of arms 40. The arms 40 may be movable and may include joints.

FIG. 11 discloses readings or output of a magnetometer 12 b in function to a rotation angle A of the magnetic source. A reference sinus wave 28 b and actual sensing sinus wave 29 b have a different phase angle C. The phase angle C can be determined despite the fact that amplitudes H1 and H2, i.e., strengths of the magnetic fields at the reference point and at the new changed location, are different. Thus, FIG. 11 illustrates that the position determination can be done without examining strength values of the magnetic fields. In other words, values of magnetic flux density E, i.e., sensed Tesla (T), have no significant importance to the determination of the phase angles.

Although the present embodiments have been described in relation to particular aspects thereof, many other variations and modifications and other uses will become apparent to those skilled in the art. It is preferred therefore, that the present embodiments be limited not by the specific disclosure herein, but only by the appended claims 

1. An apparatus for detecting change of position of a drilling tool of a rock drilling rig during drilling when the drilling tool is rotated around its longitudinal drilling axis, the apparatus comprising: at least one magnetic source mounted to the rotatable drilling tool and configured to generate rotating magnetic field, and wherein a direction of axis of the rotating magnetic field deviates from the drilling axis; at least two magnetometers configured to sense the rotating magnetic field generated by the magnetic source; at least one control unit configured to receive sensing data from the magnetometers and being configured to examine the rotating magnetic field; and at least a first magnetometer and a second magnetometer, which are both located external relative to the drilling tool, wherein the control unit is provided with data on position and orientation of the magnetometers, the control unit being provided with reference data including first reference sensing data of the first magnetometer, and second reference sensing data of the second magnetometer, when the magnetic source is located at a known reference position, and wherein the control unit is configured to compare first sensing data of the first magnetometer to the first reference sensing data for detecting a first phase angle between them, and correspondingly, to compare second sensing data of the second magnetometer to the second reference sensing data for detecting a second phase angle, and the control unit being configured to calculate a position change of the magnetic source relative to the known reference position in response to the detected phase angles and the known position of the magnetometers.
 2. The apparatus as claimed in claim 1, wherein the control unit is configured to examine the received sensing data by determining maximum strengths of the received magnetic field values and to determine a corresponding rotation angle of the magnetic source relative to the examined magnetometer, and the control unit being configured to determine the phase angles between the reference sensing data and any new sensing data by comparing the determined rotation angles of the detected maximum strength values.
 3. The apparatus as claimed in claim 1, wherein the magnetometers are located on a rock surface surrounding the drill hole being drilled.
 4. The apparatus as claimed in claim 1, wherein the control unit is provided with data on an advanced distance of the magnetic source inside the drilled hole, the control unit being configured to calculate three dimensional position data on the magnetic source in response to the detected position and the received data on the advance distance.
 5. The apparatus as claimed in claim 1, wherein the control unit is provided with sensing data from the magnetometers at several measuring points locating at different advance distances of the magnetic source inside the drilled hole, the control unit being configured to compare the calculated position data of the several measuring points and is configured to determine bending of the drilling tool in response to detected deviations in the position data.
 6. The apparatus as claimed in any claim 1, wherein the control unit is provided with data on coordinates of the magnetometers and the reference position in a work site coordinate systems, the control unit being configured to calculate coordinates of the magnetic source in the work site coordinate system.
 7. The apparatus as claimed in claim 1, wherein the control unit is configured to calculate position of a face surface of the drilling tool in response to input position data of the magnetic source relative to the face surface, whereby the position of the drilling tool is examined as the position of the face surface.
 8. The apparatus as claimed in claim 1, wherein the control unit is provided with a processor configured to execute a position detection algorithm the execution of which is configured to calculate the position of the magnetic source in response to the received sensing data of the magnetometers and the input reference data and position data.
 9. The apparatus as claimed in claim 1, wherein the control unit is configured to execute the position determination without comparing strength of the detected magnetic fields.
 10. The apparatus as claimed in claim 1, wherein the magnetic source is a permanent magnet.
 11. The apparatus as claimed in claim 1, wherein the magnetic source is mounted to a drill bit located at a distal end of the drilling tool.
 12. A rock drilling rig, comprising: a movable carrier; at least one drilling boom connected movably to the carrier and equipped with a rock drilling unit, wherein the rock drilling unit includes a feed beam and a rock drilling machine supported movably on the feed beam; and at least one apparatus according to claim 1 for determining a position of the drilling tool connectable to the drilling unit; and wherein the apparatus is in accordance with the previous claims 1-11.
 13. A method of determining position of a drilling tool of a rock drilling rig during drilling operation, the method comprising: rotating the drilling tool around its longitudinal drilling axis during the drilling and feeding the drilling tool axially forward in an advance direction; detecting a change of position of the drilling tool during the drilling by means of an apparatus having at least one magnetic source mounted to the rotating drilling tool and at least two magnetometers; generating a rotating magnetic field by rotating the magnetic source together with the drilling tool); sensing the rotating magnetic field by means of the magnetometers and producing sensing data; generating reference data by rotating the drilling tool at a known reference position and detecting a first reference sensing data by means of a first magnetometer and a second reference sensing data by means of a second magnetometer; comparing first sensing data of the first magnetometer to the first reference sensing data and detecting a first phase angle therebetween and correspondingly, comparing second sensing data of the second magnetometer to the second reference sensing data and detecting a second phase angle; and calculating a changed position of the magnetic source relative to the reference position on the basis of the detected phase angles and the position data of the magnetometers and the reference position.
 14. The method as claimed in claim 13, further comprising: sensing an advanced distance of the magnetic source inside the drilled hole during the drilling; repeating the position measurement at several measuring points having different depths in the drill hole; and comparing the calculated positions of the drilling tool at the several measuring points and determining straightness of the drill hole in response to the comparison.
 15. A computer program product having program code means configured to execute the method of claim 13 when executed by a computer or a data processing device. 